Solar Kiln questions

[abrant23]

I've begun the process of building a solar kiln since running out of dried white oak for the "honey do" list. 

Yes, I've scoured the internets as well as this forum and have absorbed as much info as I could. I am starting this topic so I can gather as much info as possible in one location. 

So here it goes:

6' x 12' kiln, approx 500bd/ft capacity slap full but will be covering collector and doing smaller loads mostly. 

Paint for inside the kiln. I have a bucket of this black Jack "rubr" coating left over from a job. Can I use that to paint the inner part of the kiln?  Would the aluminum paint with a coat of black work better?

Roof/collector. Clear lexan works for that correct? I have access to a 102" wide spool of 3/16" thick stuff. Could easily cut off a 12' piece for my collector. I also have access to 1/16" thick clear I could put under the rafters for a second layer. Is this worth the effort?

Fans? One single 16" (I have one available at 1250 cfm) or two smaller ones?  Pros or cons of using single vs multiple? 

I'm sure I'll have tons more questions as I get into this project. I have a diesel powered Woodmizer lt40 I'm using to cut the wood. 

Here's a pic of my kiln progress so far, and also a pic of the table I built out of a standing dead white oak I milled and let air dry for almost two years.

 

  

[tacks Y]

Welcome aboard. I used Black Jack latex and it was fine. Did not know Lexan came in a spool also, I would use it. Please post a pic of it. Where do you call home?

[farmfromkansas]

A question, looks like a lot of trees south of the kiln.  Are you going to get enough sun there? Especially in winter when sun is low?  Looks almost exactly like my solar kiln, but maybe you will pass me up, now that farming season has caught up. 

[btulloh]

Regarding the fan question, you probably should shoot for around 3000 cfm.  Technically that's a little more than you need for 500 bd ft, but with the inevitable inefficiencies in air flow it's better to have plenty and then be able to reduce it when needed.  Two or three fans would generally be better than one, although one can work.

Good luck with your kiln build.  Looks like it's well on the way.

[abrant23]

Thanks for the responses! 

I was thinking of a 1250 cfm fan in the middle and two smaller 900 ones on each side now that you mention needing close to 3000. That way I can turn the larger one off when drying smaller loads. 

As far as the lexan goes, yes it comes on spools. They're 102" wide (you lose a couple inches on both sides that aren't the same thickness due to processing). I'm not certain the length but it's like 300' or so. We use it in sign manufacturing. Any plastic distributor or large sign supply distributor will carry it. Sabic Polymershapes is where we get ours. 

As far as the trees, once I bring the excavator back from a job site it's on currently, they'll be gone!  I should have good sun from 8:00 to 7:30 or so during the summer. 

We got a little more work done today. I'm glad the wife is on board with this project. I told her if she wants more furniture she's gotta get the kiln built first!!  She found a 5 gallon bucket of mistinted latex in a dark brown she's gonna paint the exterior with when she gets done with the primer. 🙂



 

 

[abrant23]

Welcome aboard. I used Black Jack latex and it was fine. Did not know Lexan came in a spool also, I would use it. Please post a pic of it. Where do you call home?

Here's a photo I found online of white lexan on a spool. We have two colors of white as well as Home Depot orange and clear that comes in reel quantities. 


 

[GeneWengert-WoodDoc]

Black jack will be fine.  As the floor will get very little direct solar, you might skip painting the floor.  

Fans...for a kiln with 15 layers in the stack and 3/4" stickers, and 12' long And at least 150 fpm velocity, you will need 16 Openings x 12' long x (3/4" divided by 12 to get it into feet) x 150 fpm = 1800 cfm.  Then because of leakage, we add 50%, so 2700 cfm.  This is for 500 bf.  If you have half a load, then you have too much air flow.  Having two fans is better for uniform air flow, end to end.  In your case, three speed window fans would be best so you slow down the speed with partial loads.

Two layers of clear Lexan is really good so long as they withstand uv light.  Putting one on top and the other on the bottom of the roof framing is perfect

[abrant23]

Got a little more work done on the kiln. Rafters are black and the outer layer of lexan is ready to go on. 



 

 

[scsmith42]

That's turning out very well.

A dual pane greenhouse panel works very well.  A few years back one of our members did an analysis of kiln operating temps with single versus double pane.  Here is a link to his results.

https://forestryforum.com/board/index.php?topic=84982.msg1302695#msg1302695

The results were impressive and really showed the benefits of double pane.  As Gene alluded to, if you can install two layers of your lexan with some 1/4" or so spacers in-between them you'll get much better performance.

I'm running 3 fans in my 14' kiln, and 4 fans in my 20 footers.  Yours should do ok with two fans.  I've found that the standard 20" three speed box fans work well.  Usually I have to throw them away and replace every 2 - 3 years, but they are inexpensive.  Frame your fan openings in the baffle wall so that the fans can be quickly replaced.

[farmfromkansas]

Looks very good, nice to have a young wife to help with your projects. 

[GeneWengert-WoodDoc]

A small corrections...the space between the two layers is not critical, so, using the top and bottom framing is fine...probably 3-1/2".

[abrant23]

I'm probably gonna regret this move, but rain is coming so I went ahead and put both layers of glazing on the roof. Even bent up a piece of .125 alum for a drip edge on the high side. 

Now while it's pouring this weekend I can cut the vent holes, insulate and sheathe the interior, then smear a coat of black jack on it. 

I think it's coming along nicely for a rookie!   

 

 

 

    

[btulloh]

Looks mighty nice. You'll have a dry place to work. Warm too.  Nice drip cap. Must be handy to have a metal break. 

[abrant23]

Looks mighty nice. You'll have a dry place to work. Warm too.  Nice drip cap. Must be handy to have a metal break.

Yeah, the "warm" part is what I'm going to dread!  At least I'll stay dry tho. They're forecasting 3-5" of rain depending on when this tropical stuff gets here. 
We have a 4 meter wide CNC folding machine at work that will brake up to .1875 aluminum and .125 stainless. It's very nice to have for personal projects! 
Thanks! 

[btulloh]

Sweet. 

Clouds are your new best friends. :D  (For a while anyway.)

[farmfromkansas]

That one piece glazing is really nice!  You did not mention what it cost?

[abrant23]

That one piece glazing is really nice!  You did not mention what it cost?

That's because until you asked, I had zero clue what it actually costs!  
I asked our procurement guy and we pay $2.45 a sq-ft for the clear in 3/16" thickness. It's pretty dang thick and will last a long time since it's intended for use in sign faces. 
I got the inside insulated, plastic vapor barrier up and interior plywood hung before the sun ran me out this morning. I'm a red head so I'll burst into flames if I stay in the noon time sun too long! 


 

[scsmith42]

That's looking good.  Nice savings on the collector material too!

[abrant23]

 

 

 

 Well,

The weather has turned nice so we've gotten a little more work done this weekend on the ole kiln. 

One question, how powerful should the fans "feel" when you're standing there with the door open? When I have all three set on full blast it's like a dang wind tunnel. The center fam is wired separately than the outer two so I can control them depending on species and size of load.  I don't know if that's good or bad?! 😂

Well, here's some progress pics. Gotta find another vent or two, then paint the inside of the doors. Another couple coats of paint in the outside and she'll be done! 

[btulloh]

Wait til you have a full stack of lumber sitting there with the baffle cloth and ends blocked off before making any judgements. Airflow through all parts of the stack is what counts. You can either measure it with a small anemometer or put some strips of tell-tales on the stack or just feel the flow with your hand. 

If you have too much you can reduce it. That's better than not having enough. 

Looks good. Nice work. 

[btulloh]

Nice fans. 

[GeneWengert-WoodDoc]

I have seen hundreds of kiln is the last 40 years and this is indeed one of the nicest I have seen.  Congrats.  Gene

[abrant23]

I have seen hundreds of kiln is the last 40 years and this is indeed one of the nicest I have seen.  Congrats.  Gene

Thank you sir! 
If she works as good as she looks I'll be set.....

[Mfrost459]

I like your kiln fans, nice set-up. Where did you get the fans?

[abrant23]

I like your kiln fans, nice set-up. Where did you get the fans?

Amazon. I had the larger one left over from an attic project and found the smaller ones in a two pack bundle. They're like "Ipower" or something similar. I just searched wall mount exhaust fans.